No I don't believe everthing I read on the Internet but it's hard to give you supporting evidence with the use of the net. Like I said, look it up and make up your own mind.
Since I live in upstate SC, where Michelin has its NA headquarters, Im fortunate to know a few engineers that work for them in the tire manufacturing areas.
Iíve heard this argument about OEM tires being different than aftermarket tires for some years now, so Iíve gone to the source to find out what they say about it.
The consensus that Iíve gotten from asking them:
Auto manufacturers did indeed often have tires manufactured specifically to vehicle maker specifications. However, the same tire manufacturer make/model and sized tire, whether OEM or bought as replacements later, use the very same specifications. Thatís why you can read tire reviews (ie., Tirerack.com) for a specific make/model tire that, depending on specific size, can give wide mileage variations and service levels.
So, for example, even though the tread pattern is the same, a 185/65R15 size in a particular make/model tire might give very different ride and wear results than the same tire in a 205/60R16.
I donít have any engineering document copies to prove/disprove this, but it makes sense (at least to me).